Especially for those of us with no coding background, who can’t just build/edit an app.
For example, I like using Gadgetbridge to replace my fitness tracker app: https://gadgetbridge.org/
It’s not nearly as full-featured as a regular fitness app, but it literally can’t connect to the internet so there’s no way anyone can get my health info.
How do you feel about using Syncthing? I use it to sync my notes and files between myself, but it could work in a family setting.
Does it work between two cell phones? I thought it required a server.
It does! And there’s no server, it’s all sync’d locally or encrypted over the internet. You just need to install it on both devices and point them at each other. I don’t believe it works on iphones though. Or at least without jumping through a lot of hoops.